Cynipidae

“ It need hardly be argued that this specialization has very likely been the more recent development in the evolution of the Cynipidæ. It is not unreasonable to believe that the primitive gall-wasps inhabited a wide range of plants and that these polyphagous forms have become relatively few as the numbers of the more specialized species increased. That the small percentage of the insects which are polyphagous today, which still possess the more primitive habit, are to be considered actual remnants of the ancient forms, can be readily shown. ”

“ The Cynipidae are always small, frequently minute, Insects; usually black or pitchy in colour. The simple structure of the antennae and the number of their joints are of importance as an aid in identifying a Cynipid. The mesonotum is usually remarkably convex, and has, behind, a prominent scutellum, which more or less overhangs the small metanotum and the median segment; these are perpendicular in their direction; the sculpture of these posterior parts of the alitrunk is usually deep and remarkable. The abdomen has usually only a short petiole, so as to be pseudo-sessile ”

“ Up to the present time the relationships of the genera or even species of the Cynipidæ (Hymenoptera) have been poorly understood. Species have been catalogued without much attempt to discover an arrangement which would indicate evolution, and the genera have been in large part unnatural groups containing large numbers of unassorted, diverse organisms. Moreover, few suggestions have hitherto been made as to the origins of the peculiar biologic phenomena so characteristic of the more specialized gall-wasps. ”

“ For this reason, in the publication of new specific names in Cynips, it will be wise to avoid all names that have ever been used in the family Cynipidae. Names applied to galls only, or such combinations with Cynips as antedate the description of the insect itself, have not been considered to have nomenclatorial standing and are not included in this list. Thruout these references, Dalla Torre, 1893, Catalogus Hymenopterorum, volume 2 (Cynipidae) , is abbreviated to D.T. 93: ———. Dalla Torre and Kieffer, 1910, Das Tierreich 24:, is abbreviated to D.T. & K. 10: ———. ”

“ The species now accepted as true Cynips have been discovered as follows:
Nearly two-thirds of the varieties have been described since the beginning of the World War. There are almost as many varieties now known in this genus as Riley (in Bassett 1882:330) predicted in the American fauna of the entire family Cynipidae.
The great increase in known forms within the last twenty years would suggest that now we must have exhausted the ready opportunity to print “new species” after a Cynips ”

“ Altho many Cynipidae range all the way from Bakersfield in the southern end, to Shasta Springs at the extreme northern end of the Valley, and altho many of the species of the foothills and even higher elevations of the Sierras find no barrier in the latitude of San Francisco, many of the insects of the Coast Ranges have northern varieties that reach their southern limits and southern varieties that reach their northern limits near San Francisco Bay. ”

“ It is evident that the specialized host was not adopted by species of the Cynipidæ severally and at different times, but at two distinct periods, by two groups of forms, at a time about coincident with the differentiation of the tribes which those two groups now constitute. And it is as clear that the Aulacini comprise forms most like the primitive polyphagous species from which the Cynipini and Rhoditini have arisen at different times. ”

“ The accumulation of these geographic data has received some impetus from repeated analyses we have made of our field technic. By using the automobile we reach twice as much territory in a given time as we were formerly able to reach by railroad transportation. We find that the densest populations of Cynipidae are, for some reason not yet apparent to us, located on isolated oak trees or at edges of woodlands, and it is there that we now concentrate most of our efforts while in the field. ”

“ In some of these localities, as for instance in the neighborhood of our own laboratory at Bloomington, Indiana, the hybrid individuals may constitute 30 to 50 per cent of each collection. In places in the Cumberlands of Tennessee the hybrids may amount to 80 per cent or more of the cynipid populations. Whether the areas of transition among the Cynipidae are the same as those among other organisms must be determined by studies on these other groups. ”

“ A large proportion of the Cynipidæ reproduce agamically. There can be little question of the non-existence of the males of many of the species. Hartig (1840) bred almost 10,000 individuals of a single species, Dryophanta disticha, and secured only females. In spite of extensive collecting and breeding of many species of gall-wasps, both in Europe and America, no males have been found for some of them, and Adler (1881) and other workers have regularly secured galls and mature insects from the eggs of these agamic females.
The successive generations of some species are all similar and agamic ”

“ In another paper, on the phylogeny of the Cynipidæ, I am discussing this question in more detail and offering data which may be used to draw lines for natural genera. I hope to be able in the near future to revise the genera for the family. Until that time, it is surely wise not to maintain, in the description of new species, the several “genera” known as Cynips, Dryophanta, Callirhytis, Andricus, Biorhiza, Philonix, et al., species of which groups might all be described under the designation of "Andricus." ”

“ Altho eastern and western species of oak make rare contacts in the Texas Panhandle and in northeastern New Mexico, the affinities of all the Cynipidae of Texas east of the Pecos River are clearly with those of the eastern United States, while all the Cynipidae of West Texas are of more direct origin from the Arizona-New Mexico stocks. The geologic record indicates that the desert boundary between West Texas and the more eastern part of the state is more ancient than the genus Quercus. ”

“ Cynipoidea.—In this division the ovipositor issues from the ventral surface of the abdomen; the pronotum reaches back to the tegulae; the trochanter has two segments; the fore-wing (fig. 4, 2) has no stigma, but one or two areolets. The feelers with twelve to fifteen segments are thread-like and straight. All the insects included in this group are small and form two families—the Cynipidae and the Figitidae. ”

“ This same form of parthenogenesis also occurs in other species of Cynipidae unaccompanied by alternation {498}of generations. Thus in Rhodites rosae the generations resemble one another, and the male is very rare, but is still occasionally produced, [416] and the same condition exists in other Cynipidae. According to the observations of Adler, we may assume that the male, in the latter cases, is useless, the continuation of the species being effected by virgin females although males exist. Deuterotokous parthenogenesis also occurs in the sawflies, but as a comparatively rare phenomenon. ”

“ It is very likely that there are, still in existence today, many distinct species of Cynipidæ of primitive relationships and not yet discovered because of their hidden locations in plants. It promises to prove very profitable if we search widely-for these wasps among herbaceous plants which have their dead stems persisting throughout the winter, especially pithy stems of Composites of many genera. Though Lactuca has proved the most heavily infested thus far, it is very likely that other plants are also thus attacked. ”

“ The first abscissa of the radial vein of the wings of the Cynipidæ varies from an arcuate to a sharply angulate condition, some species showing a pronounced, vein-like projection into the radial cell at the apex of the angle made by the vein. Every degree of gradation between the extreme forms may be found. ”

“ Whether the degeneration of a segment that has become thus specialized ever occurs is a question to be debated for each group studied.
The dorsal plate of the second segment of the abdomen of Cynipidæ is always more developed than any of the other dorsal plates and in many. instances the plate has become so enlarged as to cover almost the entire abdomen. That this enlargement in the true gall-wasps is not the result of fusion is evidenced by the continued existence of the other plates underneath the enlarged plate. ”

“ Like the Cynipidae, they do not make a silken cocoon, but some of them that change to pupae inside the victims on which they were nourished have the power of forming oval cells in which to undergo their transformation, and they thus cause a peculiar inflation of the skin of their deceased victim, which after death still continues to serve as a protection to the destroyers. ”

“ The explanation that will suffice for Drosophila will probably need no essential modification for the gall wasps, but the Cynipidae may establish the importance of the laboratory mutations as materials from which species populations actually arise. ”

“ Nevertheless, if Jordan's Law holds as often as it would appear, species usually have close relatives in adjacent areas, whatever group of plants or animals they represent, and such close relatives are usually fertile inter se and should give rise to inter-specific hybrid individuals as often as we have found them among the Cynipidae. ”

“ Here is evidence that long-winged and short-winged species may be nearer than closely related species, for they may be alternate generations of one species.
In several of the cases cited above, we were delayed in our recognition of relationships by the peculiar hypopygial spines which, we have already mentioned, are found nowhere but among short-winged gall wasps. In connection with a generic re-arrangement which we are undertaking for the whole family Cynipidae, we have found that the hypopygial spine is one of the most constant of generic characters among the long-winged insects. ”

“ The discovery of heterogeny in the Cynipidæ dates from an observation reported in 1864 by Homer F. Bassett, librarian in the town of Waterbury, Connecticut, and a student whose long series of observations of gall-wasps were made with a degree of painstaking care unmatched by any other worker with the family. ”

“ This connection was finally established when C. V. Riley, in the spring of the same year in which Bassett found the producer of C. operator, bred the adult from the acorn-gall. It was identical with the producer of C. operator. The fact of alternation of generations in the Cynipidæ was thus completely proved. [2]
Meanwhile, B. D. Walsh (1864) had reported in great detail the discovery of two very different forms of adults, one agamic and the other bisexual, emerging at different times of the year from very similar if not identical galls of Amphibolips confluens. ”

“ It is very inconvenient to use a single binomial to cover the species and to designate the generation referred to by some phrase such as “agamic generation,” etc. These are the methods at present in use in Europe in naming these insects. I have adopted trinomials. Trinomials have been used previously to distinguish the forms of species showing a seasonal dimorphism; and, as I am showing elsewhere, alternation of generations among the Cynipidæ is merely seasonal dimorphism developed to an extreme degree in certain instances. ”

“ The adults emerge from April 27 to July 9. This is a wider range of dates of emiergence than is commonly found among the Cynipidæ and, unlike practically all of the other gall-wasps, adults of this species will sometimes emerge from a single gall at two or more dates separated by a month or more, indicating a considerable range of differences between the eggs from a single parent. The adults oviposit within a few hours after emergence, but may live for four or five days before dying.
Males and females are sometimes produced in about equal abundance. ”

“ In the case of other species, most likely for the majority of the oak-gall-producing Cynipidæ, only the alternate generations are siInilar, every agamic generation being succeeded by a bisexual generation, which in turn produces an agamic generation. Where this heterogeny occurs the origin and development of an agamic generation has been so involved with the origin and development of the alternation of dissimilar generations that the problem is more properly discussed in the section of this paper on the alternation of generations. ”

“ Although the majority of colonies are now purely female, the occasional appearance of males points to the fact that the unisexuality of the majority cannot have been of very long duration. The process of transformation of the species from a bisexual into a unisexual form, only composed of females, is obviously incomplete, and is still in process of development. The case is similar with several species of Cynipidae, which reproduce by the parthenogenetic method. In these cases the occurrence of a very small proportion of males is the general rule, and is not confined to single colonies. ”

“ Because of the poor distinction of several of the genera of the oak gall makers, it seems unwise to employ the generic titles Cynips, Callirhytis, Philonix, etc., until a careful revision of the genera of the family has been made. For that reason, I have used the name Andricus, the most meaningless of all these titles, with a number of the forms.
To distinguish the alternate generations of a species, I have had to adopt a new form of naming. It is highly unreasonable to continue to use the names given independently to each generation before the connections of the two forms were understood. ”